Recent evidence suggests that deficient central cholinergic tone may contribute to the clinical manifestations of presenile dementia (Alzheimer's disease) and senile dementia of the Alzheimer's type; cholinergic tone is thought to be less impaired in elderly subjects without dementia. The aims of the proposed study are to discover the extent to which cholinergic neurons in the brain are involved in the dementia of Alzheimer's disease and the intellectual decline that commonly accompanies the normal aging process, and to determine whether these losses can be modified by treatments that increase brain acetylcholine levels and release. Accordingly, we shall carry out bio-chemical and behavioral evaluations according to a double-blind cross-over protocol on patients with Alzheimer's disease and healthy elderly subjects before, during, and after administration of physostigmine and lecithin, both of which increase acetylcholine levels in the brain. For all subjects, the biochemical measurements will include plasma choline levels before and during lecithin ingestion; the behavioral assessment will include neuropsychological tests of cognitive and sensorimotor capacities and rating scales to monitor psychiatric status and capacity for self-care. Neuropathological examinations will be carried out whenever possible. Statistical analyses will be done by computer with heavy reliance upon correlations and multivariate analyses. The unusual cluster of resources outlined in this proposal, including expertise in neurology, nutrition, metabolism, and neuropsychology, offer an exceptional opportunity to make discoveries in the neurologic aspects of aging.